Optical lithography at UV wavelengths is the standard process for patterning 65-nm state-of-the-art devices in the semiconductor industry, and extensions to 32-nm and below are currently being explored. Advanced lithographic schemes are focused on the use of short wavelength (193 nm or 157 nm), coupled with immersion to further reduce the effective wavelength. Alternate approaches employ higher energy actinic radiation such as extreme ultraviolet (EUV) at 14.4 nm or high voltage electron beams to further improve lithographic resolution.
Mass-produced semiconductor manufacturing entered the era on nanopatterning with UV optical lithography when the smallest feature sizes crossed the 100-nm threshold. In the last two years advanced devices have had their half-pitch at 65 nm using 193-nm dry exposures, and it is widely expected to extend to 45-nm half-pitch by incorporating liquid immersion. According to the international roadmap for semiconductors (ITRS) this trend will continue unabated for at least one more decade with expected resolution decreasing to 45 nm in 2010, 32 nm in 2013, and 22 nm in 2016.
All manufacturing of integrated circuits (ICs) has been enabled by high-performance spin-on organic polymeric photoresists. The development of polyhydroxystyrene based resists was necessary to overcome high novolac absorbance at 248 nm and enable the introduction of 248 nm lithography into IC manufacturing. In a similar manner, 193-nm lithography required the development of a new methacrylate-based polymer system to overcome the high 193-nm absorbance of phenolic-based polymers. Due to the high absorbance at 157 nm of polyhydroxystyrene, polyacrylate, and polycyclic copolymer based resists, the use of any of these resists will only be possible if the coated resist thickness is under 100 nm. This has led to the development of fluorinated polymers as resist materials capable of high resolution. Liquid immersion lithography to a large extent will be able to utilize the same types of photoresists as employed in dry lithography although there are concerns about leaching of chemicals from the photoresists and the effect of that leaching on resist resolution and optical lens contamination. EUV and electron beam are also expected to employ resists similar to those described for other wavelengths.
The constant reduction in desired resolution has place significant strains on the performance of organic polymeric resists. These resists have only limited success in sub-32 nm patterning due to their high levels of line width roughness (LWR), reduced sensitivity, and general resolution failure. This loss of resolution has been explained by diffusion of the photoacid. The initial distribution of the exposure-generated acid can diffuse outside of the patterned area; reduce the latent image chemical contrast, and effectively blurring the final resist image which leads to reduced resist resolution.
Accordingly, a need exists for techniques and materials that can aid in overcoming the problems associated with using, and enhancing the performance of, resists in patterning nanosized features for applications such as electronics manufacturing.